Mass selective axial ejection (MSAE) is a technique used in linear ion guides of mass spectrometers to select and eject ions along the axis by applying a radial excitation. Ions are trapped radially by an RF (radio-frequency) quadrupole field and axially by static DC (direct current) potentials applied at the ends of the ion guide. An axial force arises due to a pseudo-potential that develops axially at the fringe region of the ion guide, that is dependent on the amplitude of radial excitation. When the amplitude is high, radially excited ions are ejected.